The invention relates to a steering column for a motor vehicle comprising a first and a second part, which, in the event of a vehicle crash, are dislocatable relative to one another in a displacement direction. At least one absorption element acts between these two parts for the absorption of energy during the displacement with respect to each other of the two parts, and at least one switching unit includes a switching piece switchable between a passive and an active switched position. The extensiveness of the energy absorbed during the displacement with respect to each other of the two parts differs in the passive and in the active switched position of the switching piece.
Steering columns for motor vehicles conventionally comprise a jacket unit (also referred to as “jacket tube”) by which is rotatably bearing supported the section of the steering spindle adjoining at the steering wheel end. Current developments of steering columns are most commonly adjustable in order to make possible adjusting the position of the steering wheel to the seating position of the driver. These steering columns are frequently length- as well as height- or inclination-adjustable. There are, in addition, also steering columns that are adjustable only in the longitudinal direction or only in the direction of height or inclination. The steering column can be adjusted in the opened state of a clamping mechanism and in the closed state of the clamping mechanism the set position of the steering column is secured in position. For setting the steering column in the opened state of the clamping mechanism, the jacket unit is appropriately displaced relative to a support unit via which the steering column can be connected with the chassis of the motor vehicle. For the length adjustment of the steering column, the steering spindle comprises telescopable sections and for the height or inclination adjustment of the steering column, it comprises sections that can be swiveled relative to one another.
In the event of a vehicle crash, the steering column is said to be shifted based on the corresponding energy absorption. It is known to provide for this purpose two parts dislocatable relative to one another in a displacement direction, wherein the displacement direction extends in general parallel to the direction of the length adjustment of the steering column, thus parallel to the section of the steering spindle adjoining at the steering wheel end. Between the two parts, dislocatable relative to one another in the event of a crash, acts at least one energy absorption element in order to attain a predetermined energy absorption.
The two parts dislocatable relative to one another in the event of a crash can be, for example, the support unit, which forms a type of carriage, and a chassis unit rigidly affixed on the vehicle chassis relative to which the carriage is displaceably supported. Such a formation is disclosed, for example, in WO 2006/042604.
On the other hand, in the device disclosed in WO 2007/048153 the two parts dislocatable relative to one another in the event of a crash are formed by the jacket unit, rotatably supporting the steering spindle, and the support unit. In the closed state of a clamping mechanism, toothed arresting elements are in engagement with one another, of which the one arresting element is connected with the support unit such that it is nondisplaceable relative to the longitudinal direction of the steering column, and of which the other arresting element is connected across an energy absorption element with the jacket unit. During normal operation, this connection with the jacket unit is also nondisplaceable. In the event of a crash, the arresting element can be dislocated in the longitudinal direction of the jacket unit with the absorption of energy. In the case of this steering column, further embodiment examples are described, in which the connection of one or several arresting elements with the support unit takes place across a pyrotechnical switching unit. By this unit, the arresting element can be raised from the arresting element connected with the jacket unit via the energy absorption element in order to change the energy absorption characteristic in the event of a crash.
A change of the extent of the energy absorption in the dislocation with respect to each other of the two parts of the steering column in the event of a crash can be desired as a function of several different parameters, for example as a function of the weight of the driver or as a function of whether or not the driver is buckled in.
In the steering column disclosed in EP 1 479 593 B1 between two parts, dislocatable relative to one another in the event of a crash, absorption elements can be disposed which are formed by sheet metal strips that are curved in the shape of a U. At one end these sheet metal strips are all secured on the support unit bearing the jacket tube and the steering spindle. On the other end, at least one of these sheet metal strips is fastened on a chassis unit to be secured in place on the vehicle chassis. For at least one further curved sheet metal strip, the connection with the chassis unit takes place across a pyrotechnical switching unit (“pyroswitch”). The switching unit is secured on the chassis unit and the connection of the absorption element with the chassis unit is carried out across a pin-shaped switching piece of the switching unit, which, in an active switched position, engages into a loop of the absorption element and, in a passive switched position, is pulled out of the loop whereby the connection of this absorption element with the chassis unit is opened. The energy absorption during the displacement with respect to each other of the two parts can thereby be switched over between a higher level and a lower level. A similar, controllable energy absorption arrangement is also disclosed in EP 1 707 471 A1. The absorption elements are here developed as tear strips. For at least one tear strip, the connection with a vehicle body-stationary securement part can be opened and closed through a pyroswitch in order to affect the absorption characteristic.
A further steering column with absorption characteristic variable in the event of a crash is disclosed in EP 1 187 752 B1. Between the two parts of the steering column, becoming dislocated in the event of a crash, function U-shaped curved holding strips acting as energy absorption elements. At least one bolt for the connection of the absorption element with one of the two parts can be made ineffective through a pyrotechnical element in order to vary the absorption characteristic.